Suspended Particle Composition as a Tool for Diagnosing Enhanced Algal Growth
from Eutrophication in Large Rivers

Although it is clear that humans have substantially increased nutrient inputs to large rivers across North America, attention has focused on the ecological impacts of those nutrients in downstream estuarine or coastal marine environments, where decreased turbidity allows obvious blooming of algae. Much less attention has been paid to whether increased nutrients directly affects fluvial ecosystems, largely because high and variable suspended sediment loads and short residence times have complicated data interpretation. Here we present suspended particle (seston) compositional data – including suspended solid concentration, % carbon, % nitrogen, δ 13C, δ 15N, chlorophyll, concentration and phaeopigment concentration – from the 2004-2006 EMAP Great River Ecosystems project. Seston composition suggests that most sites in the three Great Rivers studied may have higher ratios of autochthonous (aquatic algae and macrophytes) to allochthonous (terrestrial plants and soil) organic matter loads than either selected reference sites (studied in 2006) or than prisitine large rivers of the Amazon Basin. Algal concentrations appear to be most elevated in the Upper Mississippi, followed by the Ohio River and finally the Missouri River. We present preliminary metrics for assessing whether algal concentrations are enhanced relative to a minimally-impacted state.